I'm adding it to the wishlist.

The fastest way is to use the border-radius CSS attribute. This would work at least in Firefox, Safari, Chrome, Opera, and IE 9.

Please see the 6.4 release. Rounded corners are now available for Scheduler, Month, and Bubble.

Because it's implemented using border-radius, it's not working in IE 8 and previous.

In the Calendar, there is a special implementation that uses a fallback solution for the older IE versions. However, it's quite DOM-heavy and makes CSS styling very difficult so I won't be porting it to the other controls.

Thanks ;)